How to create a simple web API

Refer Below Article,

https://www.c-sharpcorner.com/blogs/consume-web-api-in-asp-net-using-http-client-with-basic-authentication

https://www.c-sharpcorner.com/article/introduction-to-asp-net-web-api/

https://dotnettutorials.net/course/asp-net-web-api/

https://www.dotnettricks.com/learn/webapi/content-negotiation-in-asp-net-web-api

https://www.youtube.com/watch?v=0pcM6teVdKk

From the information that you provided it sounds like you are looking for a document caching system. You can use the LEADTOOLS Document SDK to create your own caching system to store and manage documents.

https://www.leadtools.com/help/sdk/dh/to/document-toolkit-and-caching.html

Each document will have its own unique identifier that will be used to distinguish between the different documents.

public void DocumentIdExample() 
{ 
	var cache = GetCache(); 
 
	var policy = new CacheItemPolicy(); 
	policy.AbsoluteExpiration = DateTime.Now + new TimeSpan(0, 0, 10); 
	policy.SlidingExpiration = new TimeSpan(0, 0, 10); 
 
	var options = new LoadDocumentOptions(); 
	options.Cache = cache; 
	options.CachePolicy = policy; 
 
	string documentId = null; 
 
	using (var document = DocumentFactory.LoadFromFile(@"C:\LEADTOOLS22\Resources\Images\Leadtools.pdf"), options)) 
	{ 
		document.AutoDeleteFromCache = false; 
		documentId = document.DocumentId; 
		document.SaveToCache(); 
	} 
 
	var loadFromCacheOptions = new LoadFromCacheOptions(); 
	loadFromCacheOptions.Cache = cache; 
	loadFromCacheOptions.DocumentId = documentId; 
	using (var document = DocumentFactory.LoadFromCache(loadFromCacheOptions)) 
	{ 
		if (null != document) 
		{ 
			document.AutoDeleteFromCache = true;//will be deleted 
		} 
	} 
}

public ObjectCache GetCache() 
{ 
	// Create a LEADTOOLS FileCache object 
 
	var cacheDir = Path.Combine(@"C:\LEADTOOLS22\Resources\Images\cache"); 
	if (Directory.Exists(cacheDir)) 
		Directory.Delete(cacheDir, true); 
 
	Directory.CreateDirectory(cacheDir); 
 
	var cache = new FileCache(); 
	cache.CacheDirectory = cacheDir; 
 
	return cache; 
}

public void PrintOutDocumentInfo(LEADDocument document)
{ 
	Console.WriteLine("General"); 
	Console.WriteLine("  DocumentId:" + document.DocumentId); 
	if (document.Uri != null) 
		Console.WriteLine("  Uri:" + document.Uri); 
	Console.WriteLine("  Name:" + document.Name); 
	Console.WriteLine("  CacheStatus:" + document.CacheStatus); 
	Console.WriteLine("  LastCacheSyncTime:" + document.LastCacheSyncTime); 
	Console.WriteLine("  IsReadOnly:" + document.IsReadOnly); 
	Console.WriteLine("  IsLocal:" + document.IsLocal); 
	Console.WriteLine("  MimeType:" + document.MimeType); 
	Console.WriteLine("  IsEncrypted:" + document.IsEncrypted); 
	Console.WriteLine("  IsDecrypted:" + document.IsDecrypted); 
	Console.WriteLine("  UserData:" + document.UserData); 
	Console.WriteLine("Cache"); 
	Console.WriteLine("  HasCache:" + document.HasCache); 
	Console.WriteLine("  AutoDeleteFromCache:" + document.AutoDeleteFromCache); 
	Console.WriteLine("Metadata"); 
	foreach (var item in document.Metadata) 
		Console.WriteLine("  {0} {1}", item.Key, item.Value); 
 
	Console.WriteLine("Documents"); 
	Console.WriteLine("  Count:" + document.Documents.Count); 
	foreach (var childDocument in document.Documents) 
	{ 
		Console.WriteLine("    Name:" + childDocument.Name); 
	} 
 
	Console.WriteLine("Pages"); 
	Console.WriteLine("  Count:" + document.Pages.Count); 
 
	for (var pageNumber = 1; pageNumber <= document.Pages.Count; pageNumber++) 
	{ 
		var page = document.Pages[pageNumber - 1]; 
 
		Console.WriteLine("    PageNumber:" + pageNumber); 
		Console.WriteLine("      OriginalPageNumber:" + page.OriginalPageNumber); 
		Console.WriteLine("      OriginalDocumentName:" + page.Document.Name); 
		Console.WriteLine("      Size:{0}", page.Size); 
	} 
 
	Console.WriteLine("--------"); 
} 

Here are the steps:

1. In your Web API, get data from the database based on an "id"
2. Data is passed to a library that will create the PDF. For this, you will need a PDF creator library
3. PDF then probably should be uploaded to a shared folder or drive 
4. This URL can be now passed back to the client to download it 

Hope it helps!